The present invention relates to a synthetic resin molding apparatus for efficiently manufacturing products molded of synthetic resin.
Generally, a process of pouring a resin solution into a molding assembly to produce a synthetic resin molding comprises, for example, the steps of setting a covering sheet in a mold assembly composed of male and female mold dies, closing the mold assembly by moving the male and female mold dies relatively toward each other, pouring a resin solution into the mold assembly, and opening the mold assembly in order to remove the molded product.
After the resin solution has been poured into the mold assembly, it takes a few minutes for the poured resin solution to be hardened, and this time interval is a time loss in the entire molding process. Attempts have been made to increase the rate of production by interconnecting molding stations for effecting the molding steps with conveyors and delivering a number of mold assemblies on the conveyors so that the molding steps can successively be carried out.
Products molded of synthetic resin include large-size moldings such as automotive instrument panels. Mold assemblies for molding such large-size products are expensive, and the number of such mold assemblies used is limited so as to lower the cost of molded articles. According to one proposal, two mold assemblies are employed, and these mold assemblies are alternately shuttled for molding operation (see Japanese Laid-Open Patent Publication No. 59(1984)-229325). However, the proposed system has a limitation on the reduction of the cycle time.
An effort to shorten the time required to carry out various operations associated with the opening and closing of the mold assembly is also one of the important factors necessary to increase the efficiency of molding production. When an automotive instrument panel, in particular, is to be molded, an attachment and a duct have to be assembled in the male mold die in order to fabricate an instrument panel region where meters are to be housed, and a covering sheet having an embossed pattern on its surface has to be set in the female mold die, before the mold assembly is closed. Since the mating surfaces, i.e., the product forming surfaces, of the male and female mold dies face each other, however, the above-mentioned components cannot easily be set in the mold dies, and hence the production efficiency will not be increased substantially.
Japanese Laid-Open Patent Publication No. 58-38417 discloses swingable die holders to which upper and lower mold dies are fixed. With the disclosed arrangement, however, the upper and lower mold dies supported on the die holders cannot be tilted through sufficient angles to allow easy setting of necessary components. Furthermore, the ease with which the components are set is not increased substantially as the upper and lower mold dies are tilted in the same direction.
Some molded products such as instrument panels have undercuts. To mold such an article, a slide core is employed to give an undercut configuration to the molding. If an undercut were to be formed by a mold die, it would become difficult to remove the molded product from the mold assembly depending on the depth of the undercut formed.
Where a mold die having a slide core is moved to mold a product of synthetic resin, a problem is posed by various tubes and hoses such as hydraulic hoses connected to a cylinder which moves the slide core back and forth and tubes connected to the mold die for supplying and discharging cooling water. These tubes and hoses make up a complex system and cannot be serviced well since they are connected in such a manner to allow the mold die to move unobstructedly. To avoid such a drawback, the tubing on a station is connected to the tubing on the mold die through tube couplings, and these tubings are disconnected from each other when the mold die is moved.
The tube couplings for connecting the tubings are mostly in the form of quick-connect-and-disconnect couplings of the self-sealing type which include check valves. If a product is molded of a resin foam or cellular plastic, when the tubings are disconnected under a gas pressure developed by the foaming of the resin material, the pressure in the cylinder for moving the slide core is lowered to retract the slide core from its original position. As a result, the undercut formed in the product is shaped with poor accuracy. If a covering sheet and a resin sheet are to be integrally joined, the covering sheet tends to be wrinkled, and the resulting product becomes defective.
Some mold assemblies for molding resin products such as instrument panels include a female mold die composed of a number of separate members that are separable from each other to allow a molded product to be removed easily (see Japanese Utility Model Registration Publication No. 60-13619, for example). If a unitary inseparable female mold die were used, the female mold die would be held in too intimate contact with the product which is complex in shape, and it would be time-consuming to remove the molded product from the female mold die.
The separable mold die has its own shortcoming when the mold assembly is closed. More specifically, when the separable female mold die is put together and the male mold die and the female mold die are combined to close the mold assembly, a mechanism for separating and combining the female mold die may fail to operate, or the female mold die may not fully be put together due to an error on the part of the operator. Upon such a failure, the male mold die does not mate with the female mold die smoothly, and the mold assembly may be damaged or broken.
To set a covering sheet in the separable female mold die, the covering sheet is sometimes attracted under vacuum to the female mold die so that the covering sheet is intimately held against the product forming surface of the female mold die. To the separable members of the female mold die, there are connected pipes of an evacuating circuit for attracting the covering sheet under vacuum to the female mold die. Unless these pipes are carefully arranged with respect to the female mold die, they are liable to crack, leaking the air pressure, because the separable female die members are repeatedly separated and put together. Inasmuch as the pipes are connected respectively to the separable female mold die members, the number in parts used of the mold assembly is large.